A reanalysis of archived chromium-54 nuclear data reports that excited states have lifetimes 16% to 27% higher than historical values after the calculation was rerun with SRIM rather than LSS stopping powers. It also puts two levels under fresh scrutiny: the 3.786-MeV level is tentatively proposed as 5+1 instead of the evaluated (4)+, while the 4.043-MeV level is proposed as 6+2.
The paper re-examines a previously published 54Cr Doppler-shift attenuation measurement using the same experimental methods and procedures. The document is an arXiv preprint, version 1, dated 28 August 2026.
What changed in the analysis
The source experiment used 10-MeV alpha particles to populate 54Cr through the 51V(alpha, p-gamma) reaction. It used 99.98%-enriched 51V targets on tantalum and molybdenum backings, giving the reanalysis two earlier data sets to compare.
To repeat the calculation, the author reconstructed the original DSAM program from a printed listing, checked it against the original analyses, and upgraded it to vary stopping powers and automate the extraction of lifetimes. Two code errors were corrected, but the paper says they had negligible effect.
Stopping power is the energy lost as an ion moves through material, and it is what lets the calculation turn slowing into a time estimate. At the relevant energies, SRIM electronic stopping powers were about 60% of the older LSS values, while nuclear stopping agreed more closely between the models. Nuclear stopping dominated after a time on the order of 10 femtoseconds.
The revised numbers meet the shell model
The revised lifetimes were 16% to 27% higher than the historical values. The larger changes generally appeared among shorter lifetimes, where electronic stopping dominated the calculation.
Some combined adopted values show the scale of the revision. The lifetime at 1.824 MeV was 3.8 picoseconds, with an uncertainty of plus 1.1 and minus 0.7; at 2.620 MeV it was 0.185 picoseconds, with an uncertainty of plus or minus 0.025; and at 3.222 MeV it was 0.66 picoseconds, with an uncertainty of plus 0.08 and minus 0.07.
The revised lifetimes were then used to derive reduced E2 transition strengths, the quantities compared with shell-model calculations. For one 2+ to 0+ transition labeled Ei 835, the values were 223.5 e² fm⁴ for SM1, 171.1 e² fm⁴ for SM2, and 175(7) e² fm⁴ experimentally.
Across the comparison, the results favored the SM2 choice of effective charges, 1.3 for protons and 0.45 for neutrons, over the standard SM1 values of 1.5 and 0.5. These are the adjusted proton and neutron values used in the calculation when it estimates transition strengths. The cases discussed for 54Cr and 58Fe are not enough to support a firm general rule about effective charges.
Two levels under review
The 3.786-MeV level is the more striking case. Its lifetime is above 3.7 ps and unusually long among nearby states, and the paper proposes 5+1 rather than the evaluated (4)+ assignment. Spectroscopic confirmation is still required.
For the 4.043-MeV level, the paper proposes 6+2. Its experimental branching ratios and lifetime agree with that shell-model state, whereas the 5+1 interpretation corresponds to a shell-model lifetime two orders of magnitude longer. Further spectroscopy is needed to test the proposal.
What comes next
The findings remain tied to a reanalysis of existing data, not a new independent lifetime measurement. The revised values change the interpretation of the 54Cr measurements, but they do not by themselves settle the two spin assignments.
The authors recommend a new recoil-distance measurement of the 4+1 lifetime, saying that method is better suited to lifetimes of about 3 or 4 ps. The shell-model trend also leaves open a possible unobserved 0+ state at about 3.3 MeV, although a deficiency in the model is also considered possible.
The preprint's practical message is limited but important for this dataset: older LSS-based lifetimes should be reviewed case by case rather than treated as fixed reference values. The broader questions, including how widely the effective-charge preference applies, remain open.
The work was supported in part by Australian Research Council grants DP210101201 and DP250100400.
Paper data and sources
Original title: Doppler-shift attenuation method (DSAM) lifetimes in $^{54}$Cr - a re-evaluation
Authors: Andrew E. Stuchbery
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-28
DOI: Not available
Original paper · Full text